1. Field of the Invention
The present invention relates to an apparatus and method used for a grinding tool that uses a grinding surface comprising a surface of a tool base on which abrasive grains are discretely formed, to measure the amount of projection of each of the abrasive grains.
2. Description of the Related Art
In the field of grinding work, a non-porous grindstone or a porous grindstone is commonly used as a grinding tool. The non-porous grindstone uses a grinding surface comprising a peripheral surface of a grindstone base 11 to which abrasive grains 20 are stuck using a binder 13, for example, as shown in FIG. 5. If such a grindstone 10 is used for grinding work, the grindstone 10, which is shaped like a disk or a cylinder, is rotated at a high speed in the direction of an arrow A, for example, as shown in FIG. 6. Then, while abutting a grinding surface of the grindstone 10 against a surface of workpiece 30 to be ground, the workpiece 30 is moved at a constant speed in the direction of an arrow B. Thus, the ground surface of the workpiece 30 is cut to a fixed depth D by the abrasive grains 20. The surface of the workpiece 30 is thus ground. Reference numeral 31 denotes chips resulting from the cutting by the abrasive grains 20.
In grinding work of this kind, the quality of the ground surface of the workpiece 30 depends on the condition of the grinding surface of the grindstone 10. The conditions of the grinding surface are primarily determined by the shape and size of the surface of each abrasive grain 20, functioning as a cutting edge, the distribution of the abrasive grains 20, and the amount of projection of each adhesive grain 20. Thus, large grinding streaks may remain on the ground surface of the workpiece, depending on the condition of the grindstone 20. In particular, the amount of projection of each abrasive grain seriously affects the depth of the grinding streaks. FIG. 7 is a partial enlarged view showing an example of grinding streaks 32.
Accordingly, to achieve high-quality grinding work, it is important to accurately determine the conditions of the grinding surface, i.e. the shape and size of the surface of each abrasive grain 20, the distribution of the abrasive grains 20, the amount of projection of each adhesive grain 20, and the like. In particular, the amount of projection of each abrasive grain is very important because it determines the depth of the grinding streaks.
Thus, in the prior art, for example, the measuring methods described below have been proposed. As shown in FIG. 8, a measuring instrument is prepared in which a stylus 81 is provided by modifying a dial gauge 80. Then, the stylus 81 of this measuring instrument is used to measure the height from the tip of each abrasive grain to the binder 13 at the bottom of the adhesive grain. This measuring method is described in detail in Kazuhiko YOKOKAWA and Munehiko YOKOKAWA “CBN Wheel Grinding Work Technology” (published by KOGYO CHOSAKAI; a first edition published on Nov. 1, 1988).
However, with such a conventional measuring method, the height of each abrasive grain is measured by point-contacting the stylus 81 with the bottom of the abrasive grain. Thus, the measured value varies according to where the stylus contacts the grain. It is consequently difficult to obtain an accurate measured value. Further, it is contemplated that to improve measuring accuracy, the height of the abrasive grain may be determined by making measurements at a large number of measuring points and then averaging the measured values. However, with this method, the measurement requires much time, resulting in very inefficient operations.